Dear Customer, The technique used to create your Bally shoes is known as Foxing and involves gluing a TPU shell around the entire perimeter of the shoe. This protects the part of the shoe where the upper and sole meet, and shields components from scuffs and dirt. After a certain amount of time and depending on the conditions of use, the shoe’s foxing at the flex point may become slightly detached. This detachment, whose impact is purely aesthetic, is typical of this type of construction and is accelerated by moisture and heat, as these cause the polymer to hydrolyse.